1. Field of the Invention
This invention pertains to drilling fluids for use with drill strings and drill bits for drilling bore holes penetrating into subterranean formations of the earth. More particularly, this invention relates to such drilling fluids in which carbohydrate additives are preserved from deleterious attack so as to maintain the desired rheological, lubricating and other properties of drilling fluid.
2. Description of the Prior Art
The prior art has seen the use of wide variety of different materials to prevent the destruction of integrity of drilling fluids and maintain their rheological properties so they continue to lubricate the bit, gel with stoppage so as to prevent the falling back of cuttings, reduce the filtrate loss into permeable formations with the result of water damage and the like. This is particularly the case with drilling fluids that have employed carbohydrate additives such as polysaccharides, carboxymethylcellulose and similar compounds or materials. For example, formaldehyde and paraformaldehyde have been employed as microbiocides in drilling fluids.
Chloride dioxide has been demonstrated to be an effective microbiocide; for example in the paper industry and in textile bleaching. It is known to be a powerful and effective oxidizing agent. Illustrative of the types of prior art availabe are the following: In a summary entitled "THE CHEMISTRY OF CHLORINE DIOXIDE", Messrs. Gilbert Gordon, Robert G. Kieffer and David H. Rosenblatt "Progress In Inorganic Chemistry", Volume XV, S. L. Lippard, Editor John Wiley & Sons, New York, N.Y., 1972; pages 201-286, have shown a collection of 230 references related to chlorine dioxide. There are several United States Patents such as U.S. Pat. Nos. 3,123,521 and 4,104,190, relating to chlorine dioxide. U.S. Pat. No. 3,123,521 describes a stabilized chlorine dioxide used as a commerical germicide using sodium carbonate peroxide. U.S. Pat. No. 4,104,190 describes difficulties with the prior art requiring a highly acid environment for generation of chlorine dioxide from chlorine dioxide precursors; for example in pH's of 2-3 or lower; and then describes a method of employing a chlorine emitter to effect production of chlorine dioxide at pH's in the range of 4-9. There is a wide variety of U.S. Patents relating the chlorine dioxide in a variety of uses.
In so far as we are aware, however, the prior art has not shown the inclusion in drilling fluid of a system, or a combination of components, that will effect the rapid release of ClO.sub.2 by a nonchlorine type initiator at pH&gt;8 which will maintain a bacteriostatic level of ClO.sub.2 over a protracted time interval due to the containment of the stoichiometric buffer in the system for the prevention of the deleterious attacks on carbohydrate constituents of drilling fluids.